In today's fast-paced, on-the-move society, buses are used to transport a large number of people from location to location. Bus manufacturers have continued to increase their emphasis on ergonomic factors in the design and manufacture of their vehicles. Indeed, the passenger compartment of a modem bus contains many features to improve the passenger's comfort. These features include, for example, audio and video systems, improved seats, including variable position seating, lumbar supports in the seats, increased sound insulation, and heating, ventilation, and air conditioning systems (HVAC systems) that provide a comfortable environment for a large quantity of passengers.
To condition the air of the passenger compartment, many of the HVAC systems in buses employ a heating system separate from the cooling system. Many heating systems use heat generated from the engine of the bus to heat the passenger compartment. Unfortunately, this requires the engine to be running or turned on and off to heat the passenger compartment. The cooling system typically uses a high-pressure refrigerant system. Many of these refrigerant systems have engine-belt driven compressors. While these engine-belt driven compressors are well-suited to circulate and pump refrigerant through the refrigerant system while the engine is running, they are not able to operate when the engine is turned off. As a result, the cooling system cannot cool the passenger compartment unless the engine of the bus is left running.
Unfortunately, leaving the engine running simply to condition the air in the passenger compartment wastes money and increases the pollution produced over the life of the bus. This is particularly relevant to buses because buses may be occupied while not moving for extended periods of time, such as when the bus is waiting for passengers to load the bus, specifically when the bus is waiting for the passengers to exit an event.
To address this problem with other vehicles such as over-the-road trucks, the newest trucks are manufactured with no-idle heating and air conditioning systems. The no-idle heating and air conditioning systems are able to provide cooling and/or heating of the passenger compartment when the engine of the vehicle is turned off. Such no-idle heating and air conditioning units typically use a high pressure refrigerant system with an electric powered motor-driven, variable speed compressor powered by one or more batteries, shore power and the like instead of the primary engine belt. By using a motor-driven compressor, the no-idle heating and air conditioning system is able to heat and/or cool the passenger compartment even when the engine in the vehicle is turned off.
Unfortunately, while in the engine off condition, some no-idle systems are not capable of providing both heating as well as cooling in an engine off condition using a single circuit. These systems require a second system to provide a heat source during the engine off condition, typically utilizing a fuel fired heater. Unfortunately, this increases the amount of space required for the entire HVAC system.
Another problem with standard cooling systems that these high pressure refrigerant systems use couplings which makes the system prone to leaks. Further, because the refrigeration system is not closed until assembly of the vehicle takes place within the manufacturing assembly facility, the use of this type of system further burdens the assembly manufacturer by requiring that the initial purging and charging of the refrigeration system take place within the assembly plant of the vehicle itself increasing the manufactures' costs to manufacture the vehicle and requiring the manufacturer to maintain and store a high quantity of refrigerant.
Thus, it would be appreciated in the art if a HVAC system for a vehicle could have a system that provides both heating and cooling functions without requiring the engine to be running, that is more efficient, that reduces the likelihood of leaks in the high-pressure refrigerant.